A generic method of the type mentioned above is known from WO 20120/144778 A2.
Thin-film solar cell modules comprise a rigid or flexible, plane substrate which serves as a carrier for thin layers arranged thereon. In order to produce thin-film solar cell modules, typically after application of a first layer to the surface of the substrate this first layer is ablated in a line-shaped manner at predetermined distances so as to form so-called p1 tracks with a depth equal to the thickness of the first layer (first structuring plane).
Subsequently, a second layer is applied to the surface so that the p1 tracks are filled in. So-called p2 tracks are produced parallel to and as close as possible to the p1 tracks, the second layer, but not the first layer, being ablated therein (second structuring plane).
After a third layer which fills in the p2 tracks is applied to the surface, so-called p3 tracks are produced close to the p2 tracks and p1 tracks, and the second layer and third layer, but not the first layer, are ablated therein (third structuring plane).
Together, the p1 tracks, p2 tracks and p3 tracks lying closest to one another form a transition area which separates the individual functional areas of the thin-film solar cell module, also known as structure units, from one another.
Different technologies which can be based on mechanical, chemical or thermal effects are known for generating the tracks. In so doing, the tracks should have the smallest possible distance from one another within a transition area without overlapping, much less crossing over one another.
Regardless of the technology for introducing the tracks, the substrate is thermally loaded at least when applying the layers, which can lead to permanent deformation of the substrate and, therefore, to deformation of tracks that have already been produced.
For this reason, a lower limit is set for the distance of the tracks from one another which ensures that the tracks of the different structuring planes do not overlap or intersect in spite of maximum possible deformation.
Therefore, in a typical orientation of track paths based on an outer edge of the thin-film solar cell modules, safety distances of approximately 100 to 200 μm are specified for the desired path of the tracks relative to one another. This means that the structuring tool, e.g., a scribing needle or a laser beam, is guided for the tracks within a transition area at distances parallel to the outer edge which differ from one another by approximately 100 to 200 μm depending on the track width. This results in a minimum width of greater than 200-400 μm for a transition area. In so doing, the tracks are introduced in a machining direction in alternating movement directions.
To provide a thin-film solar cell module with narrower transition areas and, therefore, improved efficiency, it is proposed in DE 10 2006 051 555 A1 that prior to or after the introduction of a new track the path of an already existing track is determined, and when introducing the new track the path of the new track is controlled relative to the path of the existing track.
Accordingly, a new track is generated whose track path corresponds to that of an adjacent track in the same transition area. In this way, the distance between the tracks can be reduced to a minimum, as is required for reasons pertaining to insulation.
The path of an existing track is advantageously determined optically; the optical detection can be carried out from the underside of the substrate and also from the coated upper side of the substrate prior to or also during the introduction of a new track.
In this case, track detection is carried out by a track position sensor which is made to follow the path of an existing track. The position of the track position sensor is used to control a reference point which follows the track position sensor at a defined distance and at which the structuring tool is directed onto the substrate. As an alternative to the track position sensor, it is also conceivable to photographically record a majority of the partially finished thin-film solar cell module and to use these photographs as a map to determine the reference point.
Track detection with a track position sensor as described in this instance has the drawback that this track position sensor must lead the reference point, i.e., the track can only be introduced in one movement direction of the machining direction, or two track position sensors must be provided and one track position sensor would have to be constantly repositioned.
Track detection of a majority of the partially finished thin-film solar cell module requires a camera with a receiver matrix having an extremely high pixel count in order to obtain a sufficient resolution for imaging an object field of corresponding magnitude, which makes the camera a very expensive measuring tool.
DE 10 2008 059 763 A1 discloses a method in which the tracks are produced in a current machining plane based on the path of an individual track of a previous machining plane, the path of this previous track is acquired by means of a sensor, and a correction value to be used for all tracks of a subsequent machining plane is formed therefrom. In this way, the deformation of a previous track relative to the ideal straight line is detected, but not the deviations of the previous tracks from one another.
EP 0 482 240 A1 also describes a method in which tracks are produced in a current machining plane based on the path of an existing track of a previous machining plane. For this purpose, the existing track is observed by a detection element and a correction signal is formed, by means of which a tool is controlled. In this case also, the tool must trail at least slightly behind the detection element in order to generate a track which is controlled by the detection signal and which is parallel to the existing track. Therefore, the detector must either be offset by the change in direction of track generation, or two detectors must be provided, or the machining must be carried out in only one directional orientation of the machining direction.
In a structuring method disclosed in WO 2008/056 116 A1, a sensor fastened to the structuring tool is likewise used to optically detect the path and position of an already existing track in a previous machining plane. The detection takes place ahead of the structuring at a machined track simultaneous with the structuring of the track in the current machining plane. The path and position of the detected track are stored intermediately and used during the next structuring process for orienting the next track to the already existing track. Accordingly, during the structuring a detection of the previous machining plane is also carried out continuously during every structuring process.
Also in WO 2010/144 778 A2 line-shaped tracks are generated in a thin-film solar cell module so as to be oriented to the path of already existing tracks. In so doing, the position of at least a first previously generated track is acquired by a camera in order to scribe a first machined track, and the position of the first machined track is also acquired by the camera subsequently in order to produce a second adjacent track near a second previously generated track depending on the position of the first machined track.
In a first scanning movement of the thin-film solar cell module, the path of at least one already existing track is acquired by the camera along the way in the machining direction so that another track which is oriented to the path of the at least one acquired track is produced during the next scanning movement. Optionally, in a second scanning movement backwards in machining direction, the path of at least one already existing track is likewise acquired by the camera so that another track which is oriented to the path of this at least one acquired track is produced during the next scanning movement. The new tracks are accordingly generated during a scanning movement in the same directional orientation as that in which the already existing tracks to which the new tracks relate were recorded. A peculiarity of the method described above consists in that during all subsequent scanning movements the track that has just been produced is always also acquired in order to determine distances between individual tracks, e.g., for calibration.
With regard to the arrangement of the tool, in this case a laser beam, in relation to the camera, two variants are indicated. On one hand, it is suggested to integrate the camera in a scanner and to direct the optical beam path and the laser beam to the workpiece by means of a shared beamsplitter. A solution of this kind seems to be possible only in theory, particularly that acquisition by means of a camera and generation of tracks by means of lasers can take place simultaneously. On the other hand, the camera is fastened to a common frame with a fixed offset relative to the scanner. Based on this offset, it can be concluded that, in practice, the same problem already described above with respect to machining in different directions occurs in this case.